最近公司想将audioToolBox硬编码率从128K,降到64K,之前使用的是LC的编码方式，64K码率的fdk_aac的软编aac_he音质很好，但是公司线上已近不用软编了，我试着配置了硬编的参数如下：
` AudioStreamBasicDescription in = {0}, out = {0};
in.mSampleRate = 44100;
in.mChannelsPerFrame = 2;
in.mBitsPerChannel = 16;
in.mFormatFlags = kAudioFormatFlagIsSignedInteger | kAudioFormatFlagsNativeEndian | kAudioFormatFlagIsPacked;
in.mFormatID = kAudioFormatLinearPCM;
in.mFramesPerPacket = 1;
in.mBytesPerFrame = in.mBitsPerChannel * in.mChannelsPerFrame / 8;
in.mBytesPerPacket = in.mFramesPerPacket * in.mBytesPerFrame;
out.mSampleRate = 44100;
out.mFormatID = kAudioFormatMPEG4AAC_HE;
out.mFramesPerPacket = 0;
out.mFormatFlags = 0;
out.mChannelsPerFrame = in.mChannelsPerFrame;`
发现一直有些轻微的噪声谁有相关的经验可以帮帮我嘛，万分感谢。